DESCRIPTION (Applicant's Description-edited) The initiating event for human breast cancer may be associated with activation of endogenous catechol estrogens (CE). These metabolites of estrone (E1) and 17-OH- estradiol (E2) can be activated to ultimate carcinogenic forms, namely CE quinones (CE-Q). Reaction of CE-Q with DNA would constitute the initiating step of tumor induction by estrogens. Normally, oxidation of CE to CE-Q is impeded by monomethylation of CE at the 2-, 3-, or 4- hydroxy group catalyzed by catechol-O-methyltransferases (COMT), which are ubiquitous mammalian enzymes. With elevated rates of CE synthesis and/or deficient methylation by COMT, CE can be oxidized to CE-Q by peroxidases or cytochrome P450. The CE-Q can react with DNA to form adducts that could initiate cancer by mutating critical genes. Determination of the level of CE and COMT in breast tissue constitutes an important type of information. In fact, the ratio of nonmethylated vs methylated CE should be higher and the level of COMT may be lower in women with breast cancer compared to women without disease. A basic assumption in this research is that a high level of nonmethylated vs methylated CE and/or a low level of COMT is a persistent characteristic of a woman susceptible to breast cancer. Therefore, the applicant proposes to (1) determine by gas chromatography/mass spectrometry the levels of CE and their monomethoxy derivatives in breast tissue from pre- and postmenopausal women with and without breast cancer; (2) determine the levels of COMT in the same tissues by an assay using [methyl-3H]S- adenosyl methionine; and (3) develop a new immunoassay for rapid, sensitive quantitation of COMT by a "sandwich" enzyme-linked immunosorbent assay (ELISA). "Normal" tissue from breast biopsies of women with and without breast cancer will be analyzed. At the end of this grant the applicant expects to have collected sufficient data on the levels of CE and COMT in breast tissue to make preliminary comparisons of women with and without this cancer. If the hypothesis proves to be correct, and altered ratios of methylated vs nonmethylated CE and/or lower levels of COMT in patients with breast cancer in comparison with women without disease are found, the investigator will seek to demonstrate in prospective studies that these data can be early biomarkers of susceptibility to cancer. Possible ways to keep as low as possible the level of unprotected CE that could be activated to ultimate carcinogenic CE-Q will be explored in continuing research. The overall, long-term goal of this research is to reduce the incidence of breast cancer through preventive approaches.